We have observed that human B lymphoblastoid cell lines express high affinity IL-4 receptors. Because tat and IL-4 can be immunosuppressive agents, we examined the regulation of IL-4 receptors on these cells in response to tat gene. We found that constitutive expression of HIV-1 tat gene in Raji cells caused elevated expression of IL-4 receptors. This upregulation was observed at both protein and gene levels. In the presence of cycloheximide, no upregulation of IL-4 receptors was observed indicating that receptor protein synthesis is required for this upregulation to take place.